A reciprocating air compressor is a positive displacement compressor that runs on the crankshaft-driven piston and cylinder to compress the air. … A two-stage compressor includes an Piston Air Compressor additional step where the atmosphere is compressed by a second, smaller sized piston to a pressure of up to 175 PSI.

Like a little internal combustion engine, a typical piston compressor includes a crankshaft, a connecting rod and piston, a cylinder and a valve head. … As the piston movements down, a vacuum is created above it. This allows outside atmosphere at atmospheric pressure to press open up the inlet valve and fill the area above the piston.